Grafting of methyl methacrylate onto poly(methyl-4-vinylbenzyl-sulfoxide-co-trichloroethyl methacrylate) is initiated by molybdenum (III) chloride in ethylene chloride. In a second step the obtained graft copolymers are grafted with styrene in the presence of chromium(II) acetate and morpholinocyclohexene in dimethylformamide. By this stepwise selective graft copolymerization technique, polymers can be tailored to give the required properties.